NEW YORK, June 24 (Reuters) - Formal negotiations between Sri Lankan authorities and international private creditors on over $12 billion in bonds are set to resume imminently after a group of bondholders signed non-disclosure agreements late last week, three sources told Reuters on Monday.

The resumption of the talks comes days after the International Monetary Fund board approved a $336 million installment of the IMF's $2.9 billion program. About $1 billion has already been disbursed.

A representative of the bondholders did not immediately respond to a request for comment.

Earlier, the group said its negotiating committee included Amundi Asset Management, BlackRock and its subsidiaries, Eaton Vance Management, Grantham, Mayo, Van Otterloo & Co (GMO) LLC, HBK Capital Management, Morgan Stanley Investment Management, Neuberger Berman, T. Rowe Price Associates Inc, and Wellington Management.

Sri Lanka in April rejected an initial bondholder proposal, citing some of its "baseline" assessments and a lack of a contingency option in the case of continued economic weakness as two main reasons for not reaching a deal.

Sri Lanka plunged into its worst financial crisis in more than seven decades in 2022 with a severe dollar shortage sending inflation soaring to a high of 70%, its currency to record lows and its economy contracting 7.3%.

The IMF bailout secured in March last year helped stabilize economic conditions.

The island nation will hold presidential elections by mid-October. (Reporting by Rodrigo Campos; Editing by Leslie Adler)